Traditionally, the discharge of compressible material from any of a, reactor, storage vessel, or container, by way of a ‘live bottom’ reclaim screw conveyor, is problematic due to the manner in which the material within the reactor or vessel bears directly on that screw conveyor, causing choking. Material flow blockages are common, as is the stalling of the reclaim and discharge screw conveyors that results from high current draws caused in turn by the load on the screw conveyor. Such ‘live bottom’ reclaim screw conveyors of the prior art comprise a single array of screw conveyors that span the full width of the material outlet.
The nature of the compressible material that is being discharged has a significant impact on the ease or otherwise with which that material may be discharged. For example, if the compressible material is additionally fibrous, or ‘stringy’, this adds to handling difficulties.
In International Patent Application PCT/AU00/00865 (WO 01/05729) there is described a process for the treatment of organic waste in which that organic waste is subjected to sequential periods of anaerobic digestion and aerobic composting, in a single vessel or reactor, as a batch process. At the end of the process it is necessary to discharge the material from the reactor so that the next batch of organic material can be introduced to the reactor. The passage and conveyance of the processed material has proven problematic when attempted by way of traditional arrangement of a live bottom screw conveyor. The processed material produced by this process has been found to be particularly fibrous, or ‘stringy’, and is consequently difficult to convey. Further, this processed material contains significant quantities of water, adding to the difficulty in efficient conveying of the material. Significant load is placed on the screw conveyors as the material to be conveyed impinges on them, in turn placing significant load on the motors and gearboxes employed in driving them. Further, as there is a significant tendency for the material being conveyed to ‘choke’ the screw conveyors this adds to the loads referred to immediately above.
Publication CN 201010339 (Changsha Design & Res Inst) describes a method and apparatus for conveying material from a hopper. A set of first screws are employed to push material across an outlet aperture of the hopper to a lower discharge transverse screw. This arrangement does not overcome the problems associated with live bottom screw conveyors as the material being conveyed bears directly on the set of first screws that extend across the full width of the hopper and convey material in a single direction. The design of the hopper provided to feed material to the screws makes no contribution to the reduction of the force and pressure the material brings to bear on the screws, placing significant load on the first screws and the single motor driving them. No mechanism is described for dealing with or reducing the moisture content of the material to be conveyed.
Japanese Publication JP 60-77034 (Asahi Sangyo KK) describes an arrangement for the smooth conveying of objects from a hopper using a “carry-out” screw conveyor, without “bridging phenomena”. An arrangement of a single, belt driven and central carry-out screw conveyor with four gear driven “scratching” screw conveyors on either side positioned at the base of the hopper is described. All the screw conveyors are arranged to be parallel. The scratching screw conveyors convey material toward the carry-out screw conveyor which is the only conveyor of the arrangement that actually conveys material from the hopper. Again, this arrangement does not overcome the problems associated with live bottom screw conveyors as the material being conveyed bears directly on the screws that extend across the full width of the hopper and convey material in a single direction. The scratching screw conveyors attempt to direct the material to the single carry-out screw conveyor but this arrangement provides an indirect method of conveying most of the material, requiring it to be first conveyed to the single carry-out screw conveyor. The design of the hopper again makes no contribution to the reduction of force and pressure the material brings to bear on the screws. Again, no mechanism is described for dealing with or reducing the moisture content of the material to be conveyed.
The apparatus of the present invention has as one object thereof to overcome substantially the abovementioned problems of the prior art, or to at least provide a useful alternative thereto.
The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.